Laser cooling and trapping of strontium atoms for experiments towards precision measurements and frequency metrology

Kurt R. Vogel

Tong Li

Eryn C. Cook

Casimir and Casimir-Polder effects are forces between electrically neutral bodies and particles in vacuum, arising entirely from quantum fluctuations. The modification to the vacuum electromagnetic-field modes imposed by the presence of any particle or surface can result in these mechanical forces, which are often the dominant interaction at small separations. These effects play an increasingly critical role in the operation of micro- and nano-mechanical systems as well as miniaturized atomic traps for precision sensors and quantum-information devices. Despite their fundamental importance, calculations present theoretical and numeric challenges, and precise atom-surface potential measurements are lacking in many geometric and distance regimes. \n \nThe spectroscopic measurement of Casimir-Polder-induced energy level shifts in optical-lattice trapped atoms offers a new experimental method to probe atom-surface interactions. Strontium, the current front-runner among optical frequency metrology systems, has demonstrated characteristics ideal for such precision measurements. An alkaline earth atom possessing ultra-narrow intercombination transitions, strontium can be loaded into an optical lattice at the “magic” wavelength where the probe transition is unperturbed by the trap light. Translation of the lattice will permit controlled transport of tightly-confined atomic samples to well-calibrated atom- surface separations, while optical transition shifts serve as a direct probe of the Casimir-Polder potential. \n \nWe have constructed a strontium magneto-optical trap (MOT) for future Casimir-Polder experiments. This thesis will describe the strontium apparatus, initial trap performance, and some details of the proposed measurement procedure.

Spakowski, Matthew D.

The use of strontium in an atom interferometer presents the opportunity to perform detailed measurements of gravitational fields, rotation rates, and clock transitions as well as other natural phenomena. Strontium can be particularly effective in atom interferometry experiments for two reasons. The first is that the intrinsic magnetic properties of strontium result in less sensitivity of the transition frequencies to magnetic noise, allowing for better measurements. Second, strontium atoms can be cooled to a lower temperature just through ordinary Doppler cooling than other atoms typically used in interferometry (e.g., rubidium). A lower temperature means less initial kinetic energy and hence lower spatial dispersion over the course of an experiment. A magneto-optical trap consisting of two primary cooling lasers and two repump lasers cools and confines strontium atoms for use in the interferometer. This thesis focuses on the repump lasers and includes the design and performance of the optical system that frequency stabilizes each laser. The system demonstrated the ability to simultaneously frequency lock the two repump lasers to the degree necessary to form a strontium magneto-optical trap.

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